The transfer case fluid should have nothing to do with the cooler ??? Did you do some voltage or continuity measurements at the coolant sensor connector ??

Oh, nothing wrong with the transfer case. After installing a new cooler, I’ll drive the X5 to a transmission shop to check fluid level. Since I’ll be there, I may get the transfer case fluid changed. The shop charged like $125 after discounts for a transfer case and transmission oil/filter change.

No measurements were taken at the sensor connector. Pin connectors are so small. I may use my mA clamp meter or find my piercing probes. Thanks!

Amazingly, a temporary fix has worked for a few days. No more coolant has been added. The transmission lines are causing the oil cooler to teeter. The transmission lines were secured temporarily with a strong wide tie wrap. Is there a bracket down by the frame to secure the transmission lines? If oil lines are secured, the cooler stays pushed into the tank mount bracket.

Coolant system overhaul complete. After 2k miles, the low coolant warning is turned off. I know the wire was intact when I checked it. It must have been broken inside. After a few more miles, it broke completely. It was an easy find when probed with a voltmeter.

The white clip has to come out carefully. Using a small screwdriver, the pins were released. Another screwdriver pushed the pins out. The broken wire was repaired. Pins were reinserted without issue. Tape and wire loom now protect the harness. Harbor Freight tube holders were installed. The transmission lines no longer teeter the oil cooler. After a test drive, no coolant leaks were seen at the oil cooler. Small holes were drilled into the belly pan low points. A leak will be visible quicker.